Safety shutter for picture projectors



April 25, 1950 A.\S. DEARBORN SAFETY SHUTTER FOR PICTURE PROJECTORS 3 Sheets-Sheet 1 Filed Aug. 15, 1946 April 25, 1950 A. s. DEARBORN 2,504,966

SAFETY SHUTTER FOR PICTURE PROJECTORS Filed Aug. 15, 1946 3 Sheets-Sheet 2 62 I I T55 A. S. DEARBORN SAFETY SHUTTER FOR PICTURE PROJECTORS April 25, 1950 5 Sheets-Sheet 3 Filed Aug. 15, 1946 152M972 for Patented Apr. 25, 1956 SAFETY SHUTTER FOR PICTURE PROJECTORS Arthur S. Dear-born, Chicago, Iii, assignor to Ampro Corporation, Chicago, Ill, a corporation of Illinois Application August 15, 1946, Serial No. 690,699

4 Claims.

This invention relates to picture projecting machines and more particularly to the shutters for protecting the film against blistering. The invention is particularly adapted for use in connection with cinematographs, but it may also be used in connection with stereopticon projectors.

The main objects of this invention are to provide a cinematograph having improved operating mechanism for actuating the film feeding claw and the usual motion picture interrupter shutter in unison; to provide an improved form of fire shutter which will automatically be in operative position Whenever the film feeding mechanism is inoperative so as to thereby protect the film against burning by heat radiated from the source of light employed for projection purposes; to provide an improved form of safety shutter adapted to traverse the path of light so as to intermittently eclipse the light beam immediately upon the stopping of the motion picture shutter and film feeding claw so as to permit the showing of a still picture Without injury to the film; to provide improved means for attracting the still picture shutter to an inoperative position during the feeding of the film; to provide improved actuating means for automatically moving the fire shutter to inoperative position when either the motion picture interrupter shutter or the still picture shutter is in operation; to provide an improved manually controlled clutch for operatively connecting said operating mechanism with either the motion picture interrupter shutter or the still picture shutter; and to provide a cinematograph of this kind having its shutters and their operating mechanism constructed and arranged so as to occupy a minimum amount of space.

An illustrative embodiment of this invention is shown in the accompanying drawings, wherein:

Figure 1 is a fragmentary side elevation of a cinematograph to which this invention is applied.

Figure 2 is a fragmentary side elevation, partly in section, taken from the rear of Figure 1, showing the improved shutters and operating mechanism.

Figure 3 is an enlarged horizontal section, taken on the line 3-3 of Fig. 2.

Figure 4 is an enlarged transverse vertical section taken on the line 4-4 of Figure 1 and showing the fire shutter in operative position.

Figure 5 is an enlarged detail, partly in elevation and partly in section, of the interrupter shutter and still picture shutter and the operating mechanism.

Figure 6 is a view similar to Figure 4 but showing the fire shutter in its operative position.

Figure 7 is an enlarged top plan view of the three shutters and the actuating mechanism which controls the fire shutter.

Figure 8 is a fragmentary vertical section taken on the line 8--8 of Figure 7.

The heat rays contained in the beam of light used in a motion picture projector will blister or burn the picture film if any given portion of the him is ailowed to remain in the path of the beam of iight for any appreciable length of time. This blistering does not occur in the case of motion picture projection because of the high speed at which the film is fed. The projected portion of the picture film is moved out of the path of the light and another portion of the film is brought into place, sixteen times per second in silent pictures and twenty-four times per second in sound motion pictures. During the pro ection of any given portion of the picture film, the beam of light is intercepted by the motion picture interrupter shutter of the pro ector a minimum of forty-eight times per second, once to make the screen dark while another section of film is being moved into the path of the light beam, and twice during the projection of the image contained on any given portion of the picture film. The necessity for this mechanical procedure is physiological. The visual apparatus does not respond instantly to a given stimulus, nor does the sensation cease immediately when the stimulus is removed. Hence, if the eye is exposed to a source whose intensity is varied rapidly, the persistence of vision may prevent the flicker from being detected. The highest frequency at which flicker is just perceptible is known as the critical frequency.

Although the eye retains an image for a sufficiently long period of time with the screen dark so that it is possible to move the picture film from a portion containing one picture to the portion containing the next picture if at least sixteen changes per second are made, it is necessary to produce a minimum of forty-eight flashes of light per second if the human eye is to register the sensation of continuous light, i. e., to avoid flicker. Therefore, since one interruption of the light is necessary while moving the film from picture to picture, the projector mechanism, to avoid the sensation of flicker, must produce a minimum of forty-eight light flashes per second regardless of the number of individual pictures projected on the screen per second, whether it be sixteen frames, as in silent motion pictures, or twentyfour frames, as in the case of sound motion pictures.

The cause of the film blisterin or burning, of

I course, is due to the fact that the heat from the heat rays contained in the beam of light from the projection lamp is absorbed faster than it is dissipated from the film by conduction through the film supporting structures and by convection through the medium of the air surrounding the film and its supporting structures. ther conditions being equal, if a period of time we allowed for dissipation of the absorbed heat equal to the time allowed for the absorption of heat, the temperature of the film and its surrounding structures would not be increased beyond that of the atmosphere surrounding .the projector and any given portion of the film might remain in the path of the light beam indefinitely, thus allowing the projection of any scene on the picture A film as a still picture. However, it is not nec-- essary to maintain the film at normal room temperature since the film will endure a considerable increase in temperature above normal room temperature before injury will occur.

Ii a rotary shutter is so placed that during its cycle of movement it intercepts the light beam somewhere between the light source and the pic-- ture film, the film and its supporting structures are not heated during the period of time sary for the passage of the shutter blade across the path of the light beam and during this period of time the heat which has been absorbed during the period of projection is being dissipated by conduction and convection as previously described. Should the rotary shutter be so constructed or so operated that the period of interception equals the period of projectticn, the him would not blister if the shutter and film are operated at motion picture speed. The period of time allowed for absorption of heat must not be too long or the temperature of the film wili rise to the critical point at which blistering will occur.

It is not necessary that the periods of inte"- ception and projection be equal, but the period allowed for dissipation must be sufficiently long to protect the film from injury and it is necessary that the interception periods be of equal duration, or very nearly so, in order to prevent the sensation of flicker.

In a flashing or interrupted light, the duration of the period of darkness has a marked effect upon the apparent brilliancy as related to the response of the human eye. The longer thes dark periods with respect to the periods of light, the less the brightness as far as response of the eye is concerned, despite the iact that the actual brilliance is at some definite value above the value apparent to the eye. It is one of the principal aims in the design of motion picture proj ectors to consume as little time in the movement of the picture film from one picture to the next as the strength of the film will allow, since the time required for this movement determines the length of time the light beam must be intercepted and the period of interception determines the apparent brilliancy of the image. The longer thetime required for film movement, the less the apparent brilliancy.

In motion picture projectors heretofore in use, many different forms of still picture safety shutters have been used. Some or" the well known types are shown in Patents Numbers 1,836,567, 1,885,631, and 2,335,436. In all such prior constructions, the safety shutter has included a blade or filter which was movable into operative position in the path of light where it was positioned so as to eclipse some of the light rays or absorb some of the heat rays to prevent injury to the film during the showing of a still pic- 4 ture. Such still picture shutters heretofore in common use have been objectionable because they cause a light loss of approximately eightyfive precent in the projection of still pictures. Furthermore, the use of a safety shutter which is positioned in the beam of light results in a diminution of light from the center to the edges of the projected image. In some instances the decrease of light from the center to the corners of the image averaged forty percent.

I have found that, by using a rotar shutter which traverses the light beam while the film is stationary, I am able to project a still. image of higher brilliancy and one in which there is no appreciable diminution of light from the center toward the edges of the image.

The accompanying drawings show only those portions of a motion picture projector which are believed necessary to a complete understanding of the three shutters and their operating mechanism.

In the form shown, the invention is applied to a projector comprising a casing on which is mounted the usual feed and take-up reels (not shown) for supporting a film 2 which is fed by sprockets 3, 4, and 5, downwardly through a vertically disposed guideway 5 and a sound reproducing mechanism 1. The necessary intermittent movement is imparted to the film by a claw 8.

Formed in the fiim guideway is the usual aperture 9 at which each frame of the film is momentarily stopped for picture projection. Directly in front of the light aperture is an adjustable lens lii supported in a mounting l i. Formed r in the casing directly behind the film guideway is a lamp housing I2 in which is mounted the usual reflector i3, projection lamp i l, and condenser l5.

Aiso mounted in the casing is an electric motor it having a speed reducer i? and a drive shaft l8 adapted to drive a vertically disposed driven shaft Iii which is operatively connected to the film feeding claw and sprockets. Interposed between the drive shaft and the driven shaft is an improved form of manually controlled clutch illustrated in Figure 5. This clutch not only controls the movement of the film but also controls the action of the improved shutters, including a motion picture interrupter shutter still" picture safety shutter 2i, and fire shutter 2 The clutch shown in Figure 5 includes tube 23 journaled in bushings in a pair oi"; fixed bearings 2.5. Fixed on the tube 23 is a gear meshing with a gear 2'? on the vertical shaft is. Mounted on the rear end of the tube is a sleeve 28 on which is supported a pair of clutch discs 29 and til. The disc carries the motion picture interrupter shutter 28 and is provided with a hub 31 through which extends a screw 32 for clamping the sleeve 28 and disc 2Q to the tube 23. The disc iii! has a hub which is keyed to the drive shaft 18 so as to be continuously driven by the motor H3 while permitted a limited axial movement relative to the drive shaft.

Supported in the rear end of the sleeve 23 is a pin (:36. having a head 35 on its forward end. A washer 3B is secured to the rear end or the pin by a screw 31 and this washer is of greater dian1eter than the sleeve 28 so as to an annular shoulder 38 formed in the bore of the hub Embracing the forward end of the pin is a spiral spring 39 which acts between the head and an annu ar shoulder to on the sleeve so as to draw the washer 3B forwardly, th reby ur ing the clutch disc 36 into frictional driving :2 engagement with the interrupter shutter 28 which in turn drives the film feeding mechanism through the parts 29, 28, and 23.

In order to disconnect the film feeding mechanism and motion picture interrupter shutter from the continuously rotating clutch disc 36, as for instance, when it is desired to project a still image, means is provided for retracting the washer 36. This means includes an axially shiftable rod 4| which is slidably supported in the tube 23. Its rear end abuts the head 35 and its forward end abuts a cam 42 mounted on a pin 43 which is rotatably supported in a bracket 44 mounted on one of the bearings 25. The pin 43 has a knurled head 45 by which it may be turned for shifting the rod 4| and pin 34 rearwardly against the action of the spring 39.

The speed of the drive shaft l8 and its connected clutch disc 36 is such that the single blade of the interrupter shutter 26 is caused to traverse the light beam for eclipsing the rays of light at the desired frequency to prevent objectionable flicker.

The still picture shutter 2i is a multi-bladed disc having preferably three blades 66 and intermediate spaces 41, each of which is sixty degrees in width, as shown in Figures 4 and 6. This shutter is mounted on a disc 48 which is rotatably supported on a boss 49 formed on the clutch disc 38.

In order to prevent the still picture shutter 2i from eclipsing the light beam when the film feeding mechanism and interrupter shutter 26 are in operation, a magnet 52 is positioned adja cent the rim of the shutter 21 in diametrically opposed relation to the light aperture 9 so that, when the still picture shutter is not in operation, one of the blades 46 stops at the magnet and the opposed recess 41 is alined with the light aperture.

Embracing the hub 33 of the clutch disc 3%} is a collar forming a support for a plurality of helical springs 52 bearing against a washer 53. The collar 5! is secured against displacement by a retaining ring 54. Extending through the hub t6 and clutch disc 36 are spacer pins 551 which are arranged to abut the washer 53 and the disc as so as to prevent the shutter 2| from following the clutch disc 86 when the latter is moved axially into frictional driving engagement with the shutter 26. When it is desired to project a still picture, the cam 42 is turned to shift the rod ll and pin 35 rearwardly so as to release the clutch disc which then slides rearwardly on the sleeve 28 under the action of the springs 52. The friction drive is sufficient to overcome the holding action of the magnet 56 and the still picture shutter is rotated at the speed of the drive shaft IS.

The fire shutter 22 is in the form of a vertically disposed plate having lugs 55 which slidably engage a guide 56 in a housing 5! of the main casing I The fire shutter normally drops to the operative position shown in Figure 4 for covering the light aperture 9 to eclipse the light beam when the drive shaft i8 is stopped. Formed in the fire shutter is an opening 58 adapted to register with the light aperture 9 when the fire shutter is raised to the inoperative position shown in Figure 6 during the operation of the projector.

The fire shutter is supported by a lever 59 of an improved actuating means 68 which is arranged to lift the fire shutter to the inoperative position shown in Figure 6 when either one of the shutters 28-2] is in operation.

Upward movement of the fire shutter 22 is lim-- ited by an adjustable stop screw 6| mounted on the top wall of the housing 51 in position to engage the upper extremity of an arm 82 formed on the fire shutter.

The improved actuating means 66, which lifts the fire shutter to inoperative position, includes the lever 59 and a lever 63, both of which are pivotally supported by a pin 64 which is mounted on a bracket 65 secured to the frame housing 51. The outer end of the lever 59 is pivotally secured to the arm 62 of the fire shutter by a pin 66, and the outer end of the lever 63 carries a counterbalancing weight 67.

The inner end of the lever 63 is connected to a lost-motion connection, including a pin 68 mounted on the lever 63 and projecting through a hole 69 in the lever 59. The hole 69 is larger in diameter than the pin 68. Extending over the pin 68 is a spring 18 having its ends bent around the lower edges of the lever arms 59-63 so as to normally position the pin 68 at the bottom of the opening 68, whereby both arms 59-63 operate as a single lever for raising the fire shutter to its inoperative position. This lost-motion connection permits an overthrow of the actuating means 68, as hereinafter described, after the fire shutter has been stopped by the screw 6|.

Formed on the lower edge of the arm 63 is a flange ll resting on a pin 72 carried by the forward leg of a yoke 13 having an extension forming an arm 14 which is pivotally secured to the bracket t5 by a pin 15. The pin 12 and flange H are held in operative engagement with each other by a spring 18 embracing the pivot pin 64. The upper end of this spring bears against the top strap of the yoke 13 and its lower end is bent around the upper edges of the levers 59-63.

Supported in the lower ends of the yoke 13 are pins 11 for supporting a pair of rollers 18!9 which co-operate with centrifugal force responsive actuating means on the rotary shutters to lift the fire shutter to its inoperative position when either one of the rotary shutters is in operation.

The improved centrifugal force responsive actuating means comprises a plurality of governor weights 88 loosely supported in overlapping relation within annular recesses 8| formed in the outer faces of the two shutter discs 29-48. One end of each weight is pivotally secured to the shutter disc by a sleeve 82 which also passes through an arcuate slot 83 formed in the next adjacent weight for limiting the outward swinging movement of the weights under the centrifggalzflorce caused by the rotation of the shutters The governor weights are confined by annular face plates 84 mounted on the outer faces of the shutter discs 29-48. The governor weights are normally retracted by springs 85. One end of each spring is anchored in a sleeve 82, as shown in Figure 5, and its other end engages an aperture 86 in the central portion of the adjacent weight. Lugs 81 formed on the face plates 84 embrace the springs adjacent their fixed ends. T0 permit the free ends of the springs 85 to move outwardly under the action of the governor weights, the face plates 84 are slotted as shown at 88.

As illustrated in Figure 5, the two rollers 18-19 ride on the rims of the discs 29-48 in position to be actuated by the outer edges of the governor assets-e weights when the weights-are thrown outwardly under centrifugal force during the rotation of the respective shutter,

As hereinbefore described,-wlrie'n-theprojector motor and its drive shaft lil are stopped, the fire shutter 22 occupies its ope1ativepo'sition,-as shown in Figure 4, so as to completelyecl-ipsethe light beam.- While the meter l6' and it's" drive shaft the e in operation, one of the r-"otary'shutthrough the connection 29; 32, 28, for' drivingal shaft 19 which in turn drives the film feed 1g sp kets and claw. While'the rho-- tion picture in ipte'r shutter 2d isin operation, its go ter. weights 38 are thrown outwardly so as to lift the roller and its connected :iereby raising the lever'iiil' So as to lift the fire shutter '22 until its opening 5?) registers with the light aperture 91 Any overthrow of the governor Weights 8E1 after the shutter arm 62 has engaged the stop pin 61 will cause the pin 690i the lever toride upwardly in theopening 69 of the lever it is desired to project a still image, the cam 12 is turned so as to shift the rod ll and pin rearwardly against the action of the spring as, thereby releasing the clutch disc- 39. Thereupon, the helical springs 92 acting against the collar 51 washer 53' force the clutch disc rearwardl into frictional" driving engagement with the still picture shutter 21'. When the clutch disc 3 movesaway from the interrupter shutter the disc stops, thereby stopping the film feeding mechanism.

he; the operation of the still picture shut-' the roller '58 is raised for again'lifting the r to inoperative position.

Upon the stopping of both of the rotatable shut-' ke drops to the position shown" in Q thereby closing thefireshutter 22. Although but one specific embodiment of this invention has been herein shown'and described:

ter 2i it o understood'that details of the construc'-' tion may be altered without departing from" ,rit oi the invention asdefined by'the io'llo claims I l. cinematograph' comprising a casing: having a film guideway provided with a light aperture;- a light source for directing light forwardly through said aperture, mechanism for intermittentl feeding a film through s'aidguideway, said being adapted to be stopped to permit on, :tion of a still image, a pair of light ors located betweensaid'lightsource and 1 e, one said inter'oeptors being ro-' said mechanism during the-feeding or the fill means operable'upon the stopping" for rotating the other of said interceptors to intermittently interrupt heat rays irom the light source topreve'nt blis of the film during the projection of a still image, and magnetic means arranged to normally" attract said other interceptor to an inoperative position out of thepath of lightduring' therota tion of said one interceptor;

2; A Cinematograph comprising a casinghavmg alight aperture, a light source' behind said aperture, a motion picture interrupter shutter and a still picture shutter arranged'co-axi'ally in'spaced relation to each other between saidlight source and said aperture, film feeding mechanism operatively connected to said interrupter shutter, an axially movable clutch disc rotatably mounted between said shutters, manually operable means for shifting said clutch discaxially into driving engagement with either one of said shutters, a fire shutter normally movable into operative position behind said aperture for eclipsing the lightbeam, and actuating means operable by either said interrupter shutter or said'still picture shutter for moving said fire shutter to-its inoperative position.

3. A cinematographcomprising a casing having a light aperture, light source behind said aperture, a motion picture interrupter shutter and a still picture shutter arranged co-axially in spaced relation to each other between said light source and said aperture, film feeding mechanism operatively connected to said interrupter shutter, an axially movable clutch disc rotatably mounted between said shutters, manually operable means for shifting said clutch disc axially into driving engagement with either one of said shutters. a fire shutter normally movable into operative position behind said aperture for eclipsing the lightbeam, and centrifugal force responsive actuating means operable upon the rotation of either said interrupter shutter or said still picture shutter for moving said fire shutter to its inoperative position.

In a motion picture projector that comprises a light source, a drive shaft adapted to be rotated continuously and film-advancing mechanism; a

pair of rotatable shutter discs disposed respectively to intermittently interrupt a projection light beam from said source during rotation, one said shutter being permanently operatively con nected to said film-advancing mechanism and having light-passing and intercepting portions arranged to pass a maximum amount of light for motion picture projection, the other said shutter being independent of said film-advancing mechanism and having light-passing and intercepting portions arranged to intercept suflicient light to prevent heat damage of an arrested film, and 4 means for selectively coupling either the first shutter and film-advancing means or the second shutter alone to said drive'shaft.

ARTHUR S; DEARBORN.

(DES CITED following r The fences are of record in the 

